Post-eruptive flooding of Santorini caldera and implications for tsunami generation

The eruption of Santorini Volcano in the late Bronze Age was one of the largest of the last 10,000 years, and it has been implicated in the decline of the Minoan civilization on Crete. The eruption emptied a large magma chamber beneath the volcano, causing a caldera to collapse. Tsunamis caused by the eruption impacted the northern coast of Crete and possibly a large extent of the eastern Mediterranean coastline. While it is now thought that the eruption did not directly cause Minoan decline, it may have been a contributing factor through destruction of shipping, harbours and maritime trade.

A newly published paper involving T.H. Druitt and K. Kelfoun of the LMV presents bathymetric data for the caldera floor of Santorini, as well as seismic cross sections of the sediment layers beneath it. The research shows that when the caldera collapsed, probably during the last phase of the eruption, it was cut off from the sea and only flooded once the eruption was over. Differences in morphology between the different breaches that today connect the caldera to the sea suggest that the sea first broke through to the northwest, where rapid inflow of water and associated landsliding cut a huge channel. Computer modelling using the LMV-generated code ‘VolcFlow’ shows that the caldera flooding would have taken less than a couple of days.

The work has implications for the origin of tsunamis associated with the eruption. Forward modelling of tsunamis at island calderas like Krakatau and Santorini is hard because the source mechanisms are normally poorly constrained. The possibility that tsunamis at Santorini were caused by caldera collapse is ruled out by the study, because the caldera was not connected to the sea during the collapse phase. Instead, the tsunamis must have been generated by the entry of large volumes of pyroclastic flows into the sea during the eruption climax.